ALSA: fireface: add protocol-specific operation to allocate isochronous resources

This commit is a part of preparation to perform allocation/release
of isochronous channels in pcm.hw_params/hw_free callbacks.

In ALSA fireface driver, the allocation of isochronous resources is
programmed in each implementation of protocol. This commit adds
protocol-specific operation for the allocation separated from
the operation to begin session.
Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

sound/firewire/fireface/ff-stream.c

@@ -156,6 +156,10 @@ int snd_ff_stream_start_duplex(struct snd_ff *ff, unsigned int rate)
 		if (err < 0)
 			return err;
 
+		err = ff->spec->protocol->allocate_resources(ff, rate);
+		if (err < 0)
+			goto error;
+
 		err = ff->spec->protocol->begin_session(ff, rate);
 		if (err < 0)
 			goto error;

sound/firewire/fireface/ff.h

@@ -113,6 +113,7 @@ struct snd_ff_protocol {
 	int (*get_clock)(struct snd_ff *ff, unsigned int *rate,
 			 enum snd_ff_clock_src *src);
 	int (*switch_fetching_mode)(struct snd_ff *ff, bool enable);
+	int (*allocate_resources)(struct snd_ff *ff, unsigned int rate);
 	int (*begin_session)(struct snd_ff *ff, unsigned int rate);
 	void (*finish_session)(struct snd_ff *ff);
 	void (*dump_status)(struct snd_ff *ff, struct snd_info_buffer *buffer);